This invention relates to a metal sulfide thin film, such as a zinc sulfide thin film, formed by thermal decomposition of a metallo-organic compound characterized by a metal-to-sulfur bond. More particularly, this invention relates to a sulfur-stabilized metallo-organic solution that is useful in forming the metal sulfide thin film.
In the electronics industry, it is known to employ elements that comprise a thin film of a metal sulfide compound. For example, zinc sulfide thin film elements are employed in electroluminescent devices. Common methods for forming sulfide thin films employ vacuum techniques, such as vacuum evaporation or sputtering, that are relatively expensive and difficult to control, particularly in mass production operations.
Metal oxide thin film elements have been formed by thermal decomposition of metallo-organic compounds having a metal-to-oxygen bond. It is also known that metallo-organic compounds having metal-to-sulfur bonds, such as metal mercaptides, similarly decompose to produce metal sulfides. However, metallo-organic deposition of sulfide thin films has heretofore been hindered because of the difficulty of forming a stable solution of the metallo-organic compound in a suitable vaporizable solvent, particularly at concentrations sufficient to produce films of desired thickness. Furthermore, it is necessary to decompose such metal-sulfur organic compounds in an inert atmosphere to avoid oxidation. However, inert atmosphere decomposition also produces carbon as a result of pyrolysis of the organic ligand, which contaminates the sulfide film.
It is an object of this invention to provide a stabilized, concentrated solution of a sulfur-bonded metallo-organic compound, such as a metal mercaptide, in a vaporizable solvent, which solution may be used to apply the compound onto a substrate for thermal decomposition to form a sulfide thin film.
It is also an object of this invention to provide an improved method for forming by thermal decomposition of a sulfur-bonded metallo-organic compound a metal sulfide thin film element having reduced carbon contamination, which method employs a stabilized, concentrated solution to apply the metallo-organic compound onto a substrate. The solution includes an agent that not only increases solubility of the metal-organic compound and enhances the stability of the resulting solution, but also reduces carbon contamination of the product metal sulfide thin film.